La protection de la vie privée des lecteurs par les bibliothécaires français

Mémoire de fin d\u27étude du diplôme de conservateur, promotion 27, portant sur la protection de la vie privée des lecteurs dans les bibliothèques françaises

GAS-LIQUID FOAM THROUGH STRAIGHT DUCTS AND SINGULARITIES: CFD SIMULATIONS AND EXPERIMENTS

ABSTRACT Some industrial processes are associated with the flow of aqueous foams inside horizontal channels. Examples are found in the oil, food and cosmetic industries. This type of flow presents an important pressure loss, originated from the shear stress exerted by the channel walls. Foam flow is one of the most complex fluids. In a macroscopic point of view, the physical-chemical interaction between the bubbles can be related to some nonNewtonian models (Bingham law, power law, etc.) or an apparent viscosity. These last can represent the internal deformations of fluid elements when shear stress is applied. An experimental facility able to create this type of flow is not so easy to design. Many parameters must be taken into consideration. So, Computational Fluid Dynamics (CFD) constitutes an ideal technique for analyzing this kind of problem. The aim of this study is to validate the use of Computational Fluid Dynamics in order to correctly predict the pressure losses and the velocity fields of a foam flowing through a straight channel and singularities (fence and half-sudden expansion). Simulations for a realistic scenario: two-phase flow, change in the surface tension, bubble size, were undertaken. Obtained results showed that simulations are not able to accurately reproduce for such a complex fluid, the important aspects of this study, such as the pressure losses and the velocity fields. Therefore, an approximation to a Bingham fluid was made. For a foam flow quality of 70% and a velocity of 2 cm/s, the numerical results are justified by experimental evidence. Experiments have been done and predictions for the flow * Address all correspondence to this author. behavior are extrapolated. Results show that the software is able to recreate the behavior of foam flow through a straight channel and singularities. However, this approach is extremely sensitive to the choice of several parameters, like the apparent viscosity, the yield stress, the viscosity consistence, etc

Unsteady behaviour of separated and reattaching flows for a backward-facing step configuration at high Reynolds numbers.

A contribution to the study of unsteady behaviour of separated and reattaching flows over a backward-facing is reported.Unsteady wall pressure and velocity field measurements are done in order to clarify the main separate Reynolds number dependencies (based on the step height and the free stream velocity) with regards to downstream external parameters (e.g. expending ratio and boundary layer thickness). The recirculation length and the secondary separation point, as well as the statistics of the velocity filelds and the surface pressure, are analysed and compared to previous studies. The experiments are performed in an optically accessible closed-loop wind tunnel with a 2mx2mx10m test section. The step height of the backward-facing step is 83mm and corresponds to an expansion ratio of 1.04, i.e. negligible inference of the upper wall. An effectively nominally two-dimensional ow is provided by the large span of 2000mm yielding an aspect ratio of 24. A set of 25 static pressure taps in parallel with 25 sub-miniature piezo-resistive Kulite XCQ-062 sensors were distributed in the middle plane downstream of the back-facing step. The unforced flows were studied using a standard two-component TSI particle image velocimetry (PIV) system with two cameras. For every flow configuration, 2000 double-frame images were recorded with a repetition rate of 7Hz. Synchronized pressure and PIV measurements were used to analysed the statistical properties as well as the streamwise time-space characteristics of separated flows. Main flow characteristics were first investigated for seven Reynolds numbers ranged from 31500 to 182600. A comparison with previous studies was done in order to highlight the expanding ratio influences on the main separation parameters. The emphasis of this work was also placed on the convective motion of the vortical flow structures. Unsteady pressure spectra indicated that in the region close to the separation point, even for high Reynolds number, the low frequency flapping motion is dominant over the high frequency mode of the large-scale vortical structure. The ability to understand the flow field unsteadiness can lead to the development of active and/or passive flow control techniques. Current works are being done searching for active control laws strategies to control these instabilities

REALMS 2 -RESILIENT EXPLORATION AND LUNAR MAPPING SYSTEM 2

The European Space Agency (ESA) and the European Space Resources Innovation Centre (ESRIC) created the Space Resources Challenge to invite researchers to propose innovative solutions for robotic space prospection with focus on autonomous Multi-Robot System (MRS). This paper proposes Resilient Exploration And Lunar Mapping System 2 (REALMS2), a MRS framework for planetary prospection and mapping. It is based on Robot Operating System version 2 (ROS 2) and uses Visual Simultaneous Localisation And Mapping (vSLAM) for map generation. The REALMS2 uses a mesh network for a robust ad-hoc network. A single graphical user interface (GUI)) controls all the rovers, providing a simple overview of the robotic mission. REALMS2 was used during the second field test of the ESA-ESRIC Challenge and allowed to map around 60% of the area, using three homogeneous rovers while handling communication delays and blackouts

Are Amphipod invaders a threat to the regional biodiversity? Conservation prospects for the Loire River

The impact of invasions on local biodiversity is well established, but their impact on regional biodiversity has so far been only sketchily documented. To address this question, we studied the impact at various observation scales (ranging from the microhabitat to the whole catchment) of successive arrivals of non-native amphipods on the amphipod assemblage of the Loire River basin in France. Amphipod assemblages were studied at 225 sites covering the whole Loire catchment. Non-native species were dominant at all sites in the main channel of the Loire River, but native species were still present at most of the sites. We found that the invaders have failed to colonize most of tributaries of the Loire River. At the regional scale, we found that since the invaders first arrived 25 years ago, the global amphipod diversity has increased by 33% (from 8 to 12 species) due to the arrival of non-native species. We discuss the possibility that the lack of any loss of biodiversity may be directly linked to the presence of refuges at the microhabitat scale in the Loire channel and in the tributaries, which invasive species have been unable to colonize. The restoration of river quality could increase the number of refuges for native species, thus reducing the impact of invader

Investigation of the dynamics in separated turbulent flow

Dynamical behavior of the turbulent channel flow separation induced by a wall-mounted two-dimensional bump is studied, with an emphasis on unsteadiness characteristics of vortical motions evolving in the separated flow. The present investigations are based on an experimental approach and Direct Numerical Simulation (Dns). The main interests are devoted to give further insight on mean flow properties, characteristic scales and physical mechanisms of low-frequencies unsteadiness. The study also aims to clarify the Reynolds number effects. Results are presented for turbulent flows at moderate Reynolds-number ranging from 125 to 730 where is based on friction velocity and channel half-height. A large database of time-resolved two-dimensional Piv measurements is used to obtain the velocity distributions in a region covering the entire shear layer and the flow surrounding the bump. An examination of both high resolved velocity and wall-shear stress measurements showed that for moderate Reynolds numbers, a separated region exists until a critical value. Under this conditions, a thin region of reverse flow is formed above the bump and a large-scale vortical activity is clearly observed and analyzed. Three distinct self-sustained oscillations are identified in the separated zone. The investigation showed that the flow exhibits the shear-layer instability and vortex-shedding type instability of the bubble. A low-frequency self-sustained oscillation associated with a flapping phenomenon is also identified. The experimental results are further emphasized using post-processed data from Direct Numerical Simulations, such as flow statistics and Dynamic Mode Decomposition. Physical mechanisms associated with observed self-sustained oscillations are then suggested and results are discussed in the light of instabilities observed in a laminar regime for the same flow configuration

REALMS: Resilient exploration and lunar mapping system.

peer reviewedSpace resource utilisation is opening a new space era. The scientific proof of the presence of water ice on the south pole of the Moon, the recent advances in oxygen extraction from lunar regolith, and its use as a material to build shelters are positioning the Moon, again, at the centre of important space programs. These worldwide programs, led by ARTEMIS, expect robotics to be the disrupting technology enabling humankind's next giant leap. However, Moon robots require a high level of autonomy to perform lunar exploration tasks more efficiently without being constantly controlled from Earth. Furthermore, having more than one robotic system will increase the resilience and robustness of the global system, improving its success rate, as well as providing additional redundancy. This paper introduces the Resilient Exploration and Lunar Mapping System, developed with a scalable architecture for semi-autonomous lunar mapping. It leverages Visual Simultaneous Localization and Mapping techniques on multiple rovers to map large lunar environments. Several resilience mechanisms are implemented, such as two-agent redundancy, delay invariant communications, a multi-master architecture different control modes. This study presents the experimental results of REALMS with two robots and its potential to be scaled to a larger number of robots, increasing the map coverage and system redundancy. The system's performance is verified and validated in a lunar analogue facility, and a larger lunar environment during the European Space Agency (ESA)-European Space Resources Innovation Centre Space Resources Challenge. The results of the different experiments show the efficiency of REALMS and the benefits of using semi-autonomous systems